As the old standard TV technology (CRT) has nearly reached its limits, some new display panels (LCD, PDP . . . ) are encountering a growing interest from manufacturers. Indeed, these technologies now make it possible to achieve flat color panel with very limited depth.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, the new technologies have to provide a picture quality as good as or better than standard TV technology. On the one hand, these new technologies give the possibility of flat screen, of attractive thickness, but on the other hand, they generate new kinds of artifacts, which could reduce the picture quality. Most of these artifacts are different as for TV picture and so more visible since people are used to seeing old TV artifacts unconsciously.
One of these artifacts is due to the different time responses of the three colors used in the panel. This difference generates a colored trail behind and in front the bright objects moving on a dark background mainly (or the opposite). In the case of plasma display panel (PDP), this artifact is known as “phosphor lag”.
FIG. 1 shows the simulation of such a phosphor lag effect on a natural scene with a down shift. A green trail can be seen at the top edge of the trousers of the horseman.
Taking the case of plasma panels as an example, on a plasma panel, the three phosphors have not the same properties because of the chemical differences of the phosphors. In addition the life duration and the brightness are privileged at the expense of behaviour homogeneity.
The green phosphor G is the slowest, the blue one B is the fastest and the red one R is mostly in-between. Thus behind a white object in motion, there is a yellow-green trail (right-hand side of the white block of the “displayed picture” of FIG. 2), and in front a blue area (left-hand side of the white block of the “displayed picture” of FIG. 2), as can be seen in FIG. 2.
In the future, the development of new chemical phosphor powders could avoid such problems by making the green and red phosphors quicker. Nevertheless, today it is not possible by signal processing only to completely suppress this effect but one can try to make it less disturbing for a customer. The most cumbersome is not the trail but its color.
One known solution is to compensate the colored trail while modifying the blue component in the temporal domain in order to reduce the length of the trail.
One other solution is to add a complementary trail on the color trail in order to discolor it.
These two solutions need motion estimation as the solution presented in the present document.